1. Field of the Invention
The present invention relates to the technology fields of LED luminaire driving circuits, and more particularly to an LED luminaire driving circuit with high power factor.
2. Description of the Prior Art
Recently, light-emitting diodes (LEDs) are widely applied to be the lighting device in human life. And currently, more and more families replace the traditional fluorescent lamps by LED lamps due to the issue of Energy Conservation and Carbon Reduction is more and more popular. However, since the power formation of the market electricity is AC power and the LED lamps are driven to emit light by DC power, it is necessary to dispose a power converting device between the market electricity and the LED lamps for converting the AC power to DC power.
With reference to FIG. 1, there is shown a circuit framework diagram of a BCM flyback converter with variable frequency control. The BCM (Boundary Conduction Mode) flyback converter with variable frequency control 1a shown by FIG. 1 is a peak-current-mode PWM (pulse width modulation) converter, and the engineers skilled in LED lamp driving circuit field are able to find the following drawbacks of the BCM flyback converter with variable frequency control 1a from the circuit framework of FIG. 1: (1) the voltage-sensing circuit 11a disposed at the input end of the BCM flyback converter with variable frequency control 1a would produce extra power consumption; and (2) the cut-off time of the secondary side current ID—a of the BCM flyback converter with variable frequency control 1a is fully decided by the output diode DO—a, such that the cut-off time of the secondary side current ID—a cannot be precisely predicted and controlled.
Please refer to FIG. 2, there is shown the circuit framework diagram of another BCM flyback converter with variable frequency control. The BCM (Boundary Conduction Mode) flyback converter with variable frequency control 1b shown by FIG. 2 is a constant on-time control converter, and the engineers skilled in LED lamp driving circuit field can find the following drawbacks of the BCM flyback converter with variable frequency control 1b from the circuit framework of FIG. 2: the cut-off time of the secondary side current ID—b of the BCM flyback converter with variable frequency control 1b is fully decided by the output diode DO—b, so the cut-off time of the secondary side current ID—b cannot be precisely predicted and controlled.
Referring to FIG. 3, which illustrates the circuit framework diagram of a DCM flyback converter with constant frequency control. The DCM (Discontinuous Conduction Mode) flyback converter with constant frequency control 1c shown by FIG. 3 is a voltage control converter, and the engineers skilled in LED lamp driving circuit field is able to easily know that the DCM flyback converter with constant frequency control 1c can merely be used for driving low power LED lamps because the DCM flyback converter with constant frequency control 1c includes higher switching current IQ—C under the same working power.
With reference to FIG. 4, there is shown the circuit framework diagram of a COT flyback converter with variable frequency control. The COT (Constant Off-Time) flyback converter with variable frequency control 1d shown by FIG. 4 is a peak-current-mode PWM (pulse width modulation) converter, and the engineers skilled in LED lamp driving circuit field are able to find that the COT flyback converter with variable frequency control 1d can be operated under discontinuous conduction mode, boundary conduction mode or continuous conduction mode (CCM); however, the COT flyback converter with variable frequency control 1d still includes the following drawbacks: the voltage-sensing circuit 11d disposed at the input end of the COT flyback converter with variable frequency control 1d would produce extra power consumption.
Please refer to FIG. 5, which illustrates the circuit framework diagram of a constant-frequency control flyback converter. The constant-frequency control flyback converter 1e shown by FIG. 5 is a current-clamp control converter, and the engineers skilled in LED lamp driving circuit field can easily understand that the constant-frequency control flyback converter 1e carries out the power factor correction by using the constant current (CC) error amplifier 11e, the constant voltage (CV) error amplifier 12e, the opticalcoupler feedback circuit 13e, the triangle compensation signal Vtri, and the power device driving circuit 14e to produce a PWM driving signal to the power transistor QPW′. In spite of that, the constant-frequency control flyback converter 1e still includes the following drawbacks: the entire manufacturing cost of the constant-frequency control flyback converter 1e is too expensive because the disposing of the opticalcoupler feedback circuit 13e. 
Accordingly, in view of the conventional LED lamps driving circuits all include drawbacks and shortcomings, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided an LED luminaire driving circuit with high power factor.